Rename Plone 4.2 test buildouts.

It is actually testing against the dexterity version pinned by
Plone 4.2, which is dexterity p.a.dexterity 1.2.1, not 2.
Add plone.supermodel dependency constraint: we need at least 1.1.1.

plone.supermodel 1.1.1 is the first version which includes the MetadataListDirective,
which is used by the new "searchable" directive implementation.
Drop Plone 4.1 support, since we need a newer plone.supermodel version.

The new plone.supermodel dependencies require collective.z3cform.datetimewidget>=1.1dev,
but Plone 4.1 pins it down to 1.0.5.
Therefore we can no longer support Plone 4.1 with the collective.dexterityindexer 2.x series.
Merge pull request #8 from collective/jone-drop-4.1

Drop Plone 4.1 support in dexteritytextindexer 2.x